Heat-resisting material



Patented Mar. 19, 1929.

UNITED STATES WILLIAM E. RUDER, OF SCHENECTADY, NEW YORK, ASSIGNOR TOGENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HEAT-RZESISTING- MATERIAL.

No Drawing.

My invention relates to heat resisting materials and has for its objectthe provision of a metal, which may be an alloy, capable of withstandingexceptionally high temperatures for long periods of time withoutappreciable deleterious effects from oxidation and corrosion.

Aluminum added to various alloys of iron, such as iron and chromium,iron and nickel or an alloy of iron with both chromium and nickel,produces an alloy having exceptional heat resisting qualities. It may eexposed to very high temperatures, in the neighborhood of 1200 C. forlong periods of time without showing appreciable oxidation or corrosion.Such an alloy is described and claimed in a copending application SerialNo. 478,422 to Gerald R. Brophy, filed June 17, 1921, Patent Number1,638,805, of June 28, 1927, and assigned to the same assignee as thisinvention. The aluminum, however, tends to make the alloy somewhat hardand brittle and thereby reduces its malleability and ductility so thatmore or less difiiculty is experienced in working it or drawing it intowire.

In one of its aspects my invention relates to the production of metallicarticles which are shaped by drawing or otherwise working the metal andwhich must be capable of withstanding high temperatures. In carrying outmy invention I complete the drawing or other working operations of themetal before adding the aluminum, the metal then being easily worked.Thereafter, a surface protective coating of an aluminum alloy is formedon the completed article.

In accordance with my invention I form the article from a base metalconsisting of an alloy of iron with another metal, such as chromium ornickel. Preferably an iron chromium alloy is used such as is sometimesknown as stainless iron or steel. This alloy may contain from 10 to 30%or more of chromium and may be freely drawn or worked into the desiredshape. After the article. is formed, it is subjected to a heat treatmentin the presence of aluminum whereby the aluminum is caused to penetrateor alloy with the surface of the article so as to form a protectivecoating or surface layer of an alloy of iron, chromium and aluminum.

The aluminum may be applied and caused to penetrate the surface of thearticle in any suitable manner. For example where the shape of thearticle permits, it may be placed Application filedl September 14, 1925.Serial No. 56,204.

in an oven and surrounded by a powdered mixture of aluminum with salammoniac and zinc. The oven is then closed and slowly rotated, atemperature of about 450 C. being maintained. This treatment iscontinued for about two hours after which the article is taken out andfired at a temperature of 700 to 800 C. for about 15 or 20 minutes. Thisprocess is described and claimed in Patent No. 1,155,974 to Van Aller.For wires, however, also for certain tubes, the aluminum may be moresatisfactorily applied by means of the dipping process in accordancewith which the Wire is passed through a bath of molten aluminum andthereafter fired at a suitable temperature, as described and claimed inPatent #1,409,0l7 to Ortiz.

Furthermore, for complicated shapes or fabricated articles, such as gasmantles, it may be desirable to apply the aluminum by means of aspraying process whereby the powdered aluminum is mixed with a suitableliquid binder. Such a process is described and claimed in a copendingapplication, Serial No. 19,999 to Goodwin H. Howe, filed April 1, 1925,Patent Number 1,655,269 of anuary 3, 1928, and assigned to the sameassignee as this invention. In accordance with this process the powderedaluminum is mixed with a solution of nitro-cellulose and amyl acetate orwood alcohol and the mixture applied to the surface of the article bymeans of a brush or by spraying, care being taken to apply an evencoating, and the surface of the article having been thoroughly cleanedby pickling or sand blasting. After the binder has dried, the article isfired at a suitable temperature, which may be from 750 to 900 C. forabout an hour.

Any suitable process of applying the aluminum to the surface of thearticle may be used, the important feature of my invention being thatthe aluminum is not mixed with the other metals upon the formation ofthe alloy as has heretofore been the practice, but is added subsequentlyafter the drawing or working operation has been performed.

The chromium seems to have the effect of dimlnishing considerably therate of diffusion of the aluminum into the interior of the base metal ofthe article which would ordinarily take place after continued use if abase metal of iron alone were used. This diffusion or penetration of thealuminum tends to gradually decrease the proportion of aluminum at thesurface and thus gradually leaves the surface unprotected so thatdestructive oxidation would eventually take place it preventive measureswere not taken.

It will be understood that my invention is {not limited in respect tothe particular metals employed or to their proportions or methods ofhandling except in so far as it is limited by the scope of the claimsannexed hereto.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A heat resisting metallic article consisting predominantly of ironhaving a surface layer alloyed with aluminum to form a. heat resistingcoating and an interior portion substantially free from aluminum andcontaining a material preventing penetration of the aluminum into theinterior of the article upon exposure to high temperatures.

2. A heat resisting metallic article consistiron, ch -omium andaluminum, the interior portions of said article being composed of amalleable alloy of iron and chromium;

4. A heat resisting metallic article made of a malleable alloy of ironand chromium having, its surface metal alloyed with aluminum to form aprotective coatin In witness whereof, I have hereunto set my hand this11th day of September, 1925.

WILLIAM E, RUDER.

